The molecular-electronic mechanisms by which a protein environment modifies the properties of flavin coenzymes so as to generate a specific enzyme system will be explored. Emphasis will be given to dehydrogenases (especially the flavodoxins) and oxidases. Among the problems to be investigated are the following: Amino acid sequence determination of Azotobacter flavodoxin, chemical modification of trp, lys, arg, tyr, asp and glu side chains in flavodoxins, pH dependence of flavin binding kinetics and equilibria in flavodoxins, the effect of complexation by indoles and phenols on flavin redox properties, coenzyme binding kinetics and equilibria in oxidases, redox potential measurements of oxidases, and comparison of kinetics of redox reactions between free and protein-bound flavin.